Don, KB9UMT, moderator and owner of the HamRadioHelpGroup mailing list came up with the following chart:
Year___ %Ham__US Population___# US Hams
1925___0.01%___115,829,000_____16,500
1930___0.02%___123,076,741_____19,000
1935___0.04%___127,250,232_____45,000
1940___0.04%___132,122,446_____55,788
1945___0.04%___139,928,165_____62,250
1950___0.05%___152,271,417_____81,450
1955___0.09%___165,931,202_____144,168
1960___0.13%___180,671,158_____227,500
1965___0.14%___194,302,963_____265,862
1966___0.14%___196,560,338_____268,129
1967___0.14%___198,712,056_____278,543
1968___0.14%___200,706,052_____275,628
1969___0.14%___202,676,946_____277,209
1970___0.14%___205,052,174_____279,658
1971___0.13%___207,660,677_____278,808
1972___0.13%___209,896,021_____274,389
1973___0.13%___211,908,788_____268,657
1974___0.13%___213,853,928_____271,373
1975___0.12%___215,973,199_____268,002
1976___0.13%___218,035,164_____283,473
1977___0.14%___220,239,425_____311,328
1978___0.16%___222,584,545_____350,780
1979___0.17%___225,055,487_____374,015
1980___0.17%___227,224,681_____393,353
1981___0.17%___229,465,714_____398,829
1982___0.18%___231,664,458_____408,361
1983___0.18%___233,791,994_____416,084
1984___0.18%___235,824,902_____433,921
1985___0.18%___237,923,795_____438,007
1986___0.18%___240,132,887_____433,921
1987___0.18%___242,288,918_____442,136
1988___0.19%___244,498,982_____455,642
1989___0.19%___246,819,230_____459,635
1990___0.19%___249,464,396_____466,511
1991___0.20%___252,153,092_____494,260
1992___0.21%___255,029,699_____524,782
1993___0.22%___257,782,608_____575,146
1994___0.24%___260,327,021_____614,398
1995___0.25%___262,803,276_____656,726
1996___0.25%___265,228,572_____661,775
1997___0.25%___267,783,607_____677,514
1998___0.25%___270,248,003_____676,809
1999___0.25%___272,690,813_____677,392
2000___0.25%___275,133,623_____682,240
2001___0.25%___275,279,000_____684,359
2002___0.25%___276,709,000_____685,308
2003___0.25%___278,112,000_____687,860
2004 672,622
2005 662,600
2006 654,291
Sources:
http://www.hamdata.com/fccinfo.html
http://www.ah0a.org/AH0A.html
http://www.ah0a.org/FCC/Licenses.html
http://hamcall.net/divisions_by_callsign.html
http://www.speroni.com/FCC/index.html
http://www.qrz.com/i/census.html?
http://www.jarl.or.jp/English/1_Amateur/A-1-9.htm
Don notes that the number of licensed amateurs has declined since 2003, and that the population of the U.S. has increased. If we use a figure of 300 million for the population [...]